Trans-endoscopic hydraulic balloon apparatus

ABSTRACT

A trans-endoscopic hydraulic balloon dilation apparatus includes a fluid reservoir containing a hydraulic fluid. A shaft has a lumen in fluid communication with a leading end of the fluid reservoir. A balloon is mounted on the shaft and an opening in the shaft enables hydraulic fluid to flow through the opening into or from the balloon. A piston secured to a leading end of a piston rod is slideably positioned within a lumen of the fluid reservoir. A hub secured to a trailing end of the fluid reservoir is centrally apertured to accommodate the piston rod so that a trailing end of the piston rod is external to the fluid reservoir. Displacement of the piston rod in a trailing-to-leading direction causes expansion of the balloon. Displacement of the piston rod in a leading-to-trailing direction causes deflation of the balloon. The piston can be locked into any position.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior filed InternationalApplication, Ser. No. PCT/US2008/085124 filed Dec. 1, 2008, which claimspriority to U.S. provisional patent application No. 60/991,415 filedNov. 30, 2007 which is hereby incorporated by reference into thisdisclosure.

BACKGROUND OF THE INVENTION

Trans-endoscopic balloon dilation of accessible gastrointestinal tractstrictures offers the advantage of not requiring removal of theendoscope and insertion of a different device (frequently underfluoroscopic guidance) in order to accomplish dilation. Proceduredurations are therefore minimized, patient and staff exposure toradiation is avoided, and, when the procedure is to be continued beyondthe dilation, the necessity of repeating endoscopic insertion iseliminated. The later is particularly important in minimizing risk tothe patient in those instances where initial passage of the endoscope tothe location of the stricture is difficult.

Through the endoscope, balloon dilation of tight esophageal stricturesis frequently carried out with fluoroscopic monitoring. A stricture isconsidered to be “tight” if an endoscope cannot be passed through it.Fluoroscopic monitoring of tight stricture dilation is believed to helpprevent sudden fracture or splitting of the stricture and thus reducethe risk of esophageal perforation during the dilation procedure.Currently available dilation balloons are made of transparent materialto facilitate visualization. U.S. Pat. No. 6,953,431 to Barthel, whichis incorporated herein by reference, discloses an apparatus that enablesdirect observation of the stricture wall response during balloondilation. This is an advantage unique to balloon dilation that is notpossible with other dilation techniques.

Examination and accurate measurement of an esophageal stricture can onlybe accomplished visually or endosonographically if the endoscope can bepassed completely through the stricture. Two techniques exist foraccomplishing complete stricture passage with balloon dilation. Thetraditional method is to pass and inflate successively larger balloonsacross the stricture until a diameter of 15 to 40 mm is achieved. Thelast dilation balloon is then removed and the instrument is maneuveredthrough the stricture under direct unguided operator control. Thepost-dilation 15 or 40 mm diameter stricture lumen is 5 or 6 mm largerthan the diameter of a standard video endoscope and 2 to 3 mm largerthan the diameter of an echoendoscope. However, stricture elasticity,luminal tortuosity, and frequent shelving (stepped areas along thestricture) can prevent passage of the instrument, despite an apparentlyadequate dilation.

An alternative method for accomplishing complete stricture passage withballoon dilation is the “balloon-scope train method.” The stricture isdilated to a diameter 1 or 2 mm larger than the diameter of theendoscope. The endoscope is then pushed up against the proximal end ofthe inflated dilation balloon to form a balloon-scope “train.” Thecombination of balloon and endoscope is then advanced through thestricture.

Conventional trans-endoscopic balloon dilation systems, however, requirea level of mechanical understanding and operational training that isseldom available among the individuals called upon to assemble andoperate the devices during endoscopic procedures. More specifically, thecomponents that must be collected and assembled include a shaft mountedballoon, an inflation gun, a manometer, and saline or other suitablefluid. The collection of these components and their assembly is requiredto render the currently available balloon dilation systems operational.The resulting procedural delays and device operation errors arising fromimproper assembly significantly mitigate the advantages oftrans-endoscopic balloon dilation.

Thus, there is a need for a trans-endoscopic balloon dilation systemthat does not require intra-procedure assembly of components and thedelays and errors that result therefrom. The needed device would befully assembled in a factory and it would be pre-filled with a suitablefluid for balloon dilation. Such a device would enable an operating teamto concentrate on the surgical procedure without the distraction ofassembling a tool and the problems and delays associated with suchassembly.

SUMMARY OF INVENTION

An endoscopic dilation instrument assembly comprises, in accordance withthe present invention, a hydraulic fluid reservoir in fluidcommunication with a balloon having at least one expandable orinflatable end portion. An elongate hollow shaft is provided forconnecting the balloon to the fluid reservoir, with the balloon beingdisposed in a collapsed configuration along an outer surface of theshaft. An inflation element within the fluid reservoir is operativelycoupled with the balloon for enabling the inflation of the balloon fromthe collapsed configuration to an expanded use configuration in whichthe inflation element pushes the hydraulic fluid in a distal directionaway from the trailing end of the reservoir for spreading internaltissues of a patient to facilitate access and/or viewing of the tissues.Deflation of the balloon from the expanded use configuration to thecollapsed configuration is provided in which the inflation element drawsthe hydraulic fluid in a proximal direction away from the balloon.

Pursuant to another feature of the present invention, the inflationelement comprises a piston, secured to a leading end of an elongatepiston rod, slideably positioned within a lumen of the fluid reservoir.A hub is secured to a trailing end of the fluid reservoir. The hub iscentrally apertured to accommodate the piston rod so that a trailing endof the piston rod is external to the fluid reservoir. A piston rodhandle is mounted to the trailing end of the piston rod. Displacement ofthe handle and hence the piston in a trailing-to-leading(proximal-to-distal) direction therefore causes expansion of theballoon. Displacement of the handle and hence the piston in aleading-to-trailing (leading-to-trailing) direction causes deflation ofthe balloon.

In a preferred embodiment, the inflation element includes a lockingmechanism for securing the inflation mechanism, and the diameter of theballoon by extension, in a preselected position. Although the lockingmeans may take many forms, in a preferred embodiment the locking meansincludes a plurality of ratchet members formed in the piston rod alongan extent thereof. The ratchet members of this preferred embodimentengage a ratchet plate disposed within the hub. Each of the plurality ofratchet members engage the periphery of an elongate opening formed inthe ratchet plate as the piston is displaced in a trailing-to-leadingdirection.

Another feature of the invention includes graduation markings providedon the transparent or substantially transparent, translucent fluidreservoir. The movement of the piston relative to these markingscorresponds to a predetermined volume of hydraulic fluid being expelledfrom, or drawn into, the fluid reservoir. Accordingly, the user mayposition the piston in alignment with said markings to ascertain thediameter of the balloon based on the amount of fluid therein and doesnot require direct visualization thereof. Optionally, the spacing of thegraduated markings corresponds to the spacing of the ratchet members.The graduated markings can represent the volume of fluid within thefluid reservoir or can represent the diameter of the balloon.

Furthermore, the long-standing but heretofore unfulfilled need for apre-assembled and pre-filled trans-endoscopic balloon dilation system isnow met by a yet another embodiment of the invention. The inventivestructure of this embodiment is an integrally formed, single-unittrans-endoscopic self-contained, pre-filled hydraulic balloon dilationapparatus that requires no assembly by the end user.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference should be made tothe following detailed description, taken in connection with theaccompanying drawings, in which:

FIG. 1 is a diagrammatic, side elevational view of the novel endoscopewhen the balloon is deflated;

FIG. 2 is a diagrammatic, side elevational view of the novel endoscopewhen the balloon is inflated;

FIG. 3A is a diagrammatic, side-elevation detail of the shaft andballoon wherein the balloon is inflated;

FIG. 3B is a diagrammatic, side-elevation detail of the fluid reservoirand hub;

FIG. 3C is a diagrammatic, side-elevation detail of the inflationelement;

FIG. 4A is a diagrammatic, end elevation view of a ratchet lock andrelease device wherein the ratchet plate is engaged with the trailingend of the piston, thereby locking the inflation element in apreselected position.

FIG. 4B is a diagrammatic, end elevation view of a ratchet lock andrelease device wherein the ratchet plate is rotated to disengage thetrailing end of the piston, thereby allowing the inflation element to beretracted.

FIG. 5A is a diagrammatic, end elevation view of a ratchet lock andrelease device wherein the ratchet plate is engaged with the trailingend of the piston, thereby locking the inflation element in apreselected position.

FIG. 5B is a diagrammatic, end elevation view of a ratchet lock andrelease device wherein the piston and piston rod are rotated todisengage the ratchet plate, thereby allowing the inflation element tobe retracted.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings, which form a parthereof, and within which are shown by way of illustration specificembodiments by which the invention may be practiced. It is to beunderstood that other embodiments may be utilized and structural changesmay be made without departing from the scope of the invention.

The present invention includes embodiments of a endoscopic dilationdevice 10, such as that depicted in FIGS. 1 and 2, configured tofacilitate negotiation of the scope through a stricture or otherdifficult or tortuous pathway within the body, and/or to abut theviewing port or objective lens of an endoscope face such that anatomicalstructures of interest can be viewed.

Referring now to FIGS. 1 through 3C, it will be seen that anillustrative embodiment of endoscopic dilation device is denoted as awhole by the reference numeral 10 and has leading end 10 a and trailingend 10 b. Balloon 20, typically made of a clear, non-distensible polymermaterial such as transparent polyethylene terephthalate (PET), ismounted on shaft 30, made of a flexible catheter material, near theleading end (30 a, FIG. 3A) thereof and is depicted in a deflatedconfiguration in FIG. 1 and in an inflated configuration in FIG. 2.Trailing end 30 b of shaft 30 is in fluid communication with fluidreservoir 40 having a conical leading end 40 a and a cylindricaltrailing end 40 b defined by transparent or translucent barrel 42. Fluidreservoir 40 houses hydraulic fluid 17, such as water or saline. Leadingend 10 a generally provides an atraumatic means of cannulating astricture or generally guiding the balloon through a passageway.

The illustrative balloon 20, depicted in greater detail in FIG. 3A,comprises a main portion 22 that is generally uniformly cylindrical inshape, and a tapered portion 24 toward the leading end 20 a of theballoon portion 20. The trailing end 20 b of balloon 20 is generallytruncate in shape such that the trailing end 20 b can be cinched ordrawn against the distal face of an endoscope (not shown) from which ithas been advanced, such that there is broad area of contact between theballoon and at least a substantial cross section of the endoscope face.The area of contact includes the viewing port or objective lens (notshown), and preferably, but not essentially, the light source (notshown) such that the balloon portion generally serves as an extension ofthe lens, thereby enabling the endoscopist a relatively unobstructed andundistorted view through the balloon interior, which permitsvisualization of the anatomical structures within the body conduit.

The main portion 22 of balloon 20 includes a central axis thatintersects the cross-sectional center point of the main cylindricalportion 22. Balloon 20 also includes a luminal axis that intersects theleading and trailing openings thereof. In a preferred embodiment, theluminal axis of the present invention comprises the original lumen ofthe tubing used to form balloon 20, but unlike a standard dilationballoon, is offset relative to the central axis to allow alignment withthe endoscope. Generally, it is desired that balloon 20 and outercontours of the endoscope be concentrically aligned with one another tomaximize the field of view and reduce ledges or surfaces that are proneto catch upon a shelf or stricture during advancement of theballoon-scope train.

Although having the balloon diameter closely match that of the endoscopeprovides the ideal clinical situation for introduction of theballoon-scope train, it is not necessary to the invention that theballoon and scope be of the same diameter. Often, multiple sizes ofballoons are used with a given endoscope for a single procedure, such asin esophageal dilation procedures, where attempting to fully dilate in asingle, rather than multiple stages, increases the risk of rupture. Thestandard sizes of endoscopes used in gastrointestinal procedures are8.5, 9.5 and 11.5 mm, which are generally compatible with the mostpreferred range of balloon diameters for the illustrative embodiment(10-40 mm).

Balloon 20 of the illustrative embodiment of FIGS. 1 and 2 is formed bya well-known means, such as blow molding, whereby a length of PTEtubing, sufficient in length to form the final desired length of theballoon, is placed and clamped within a mold conforming to the finalshape of the fully distended balloon. Hot air is passed through thetubing, causing the tubing to expand against the contours of the mold.The tubing and molding process parameters necessary to achieve thedesired balloon are determined by the required burst strength andrecommended pressure of the balloon, the material used, and the size ofthe balloon. One source of balloon 20 of the illustrative embodiment isAdvanced Polymers, Inc. (Salem, N.H.). The typical range of diametersfor an 8 cm long esophageal dilation balloon is generally about 6 to 19mm, with a more preferred range of 12-18 mm. Minimum specified burstpressures typically average 175 psi for a 12 mm balloon, down to about122 mm for an 18 mm diameter balloon, with the corresponding recommendedpressures being about 90 and 50 psi, respectively. Pyloric and colonicdilation balloons are typically shorter in length (e.g., 5.5 cm);however, the recommended pressures are generally the same as the longeresophageal balloons for corresponding diameters.

In certain embodiments, the proximal end of the balloon is indented.Such indentations can permit the endoscopist to lock or otherwise morecompletely engage the proximal end of the balloon with the distal end ofthe endoscope, thereby resisting rotational movement and thus minimizingrotational loss of balloon/scope alignment. One such exemplaryembodiment comprises an indentation which effectively results in acircumferential flange at the proximal end of the balloon that isconfigured to frictionally engage the distal end of the endoscope.

In the illustrative embodiment of FIGS. 1 and 2, shaft 30 includes asingle lumen that provides an infusion pathway to balloon 20, wherebywater or saline is introduced, via reservoir 40. The balloon ismaintained in a deflated state and is folded and inserted into adelivery sheath (not shown). It is then advanced from the deliverysheath into the instrument (accessory) channel of the endoscope, whichtypically is a minimum of 2.8 mm for an illustrative esophageal dilationballoon, as well as the related pyloric, or colonic embodiments in whichthe balloon is 18 mm or smaller in diameter when inflated. Examples ofother clinical applications include, but are not limited to, biliarytree, bronchial tree, neural endoscopy and the vascular system. Largerdiameter balloons, e.g., 19-20 mm, may require an instrument channel ofup 3.7 mm or greater. Typically, the balloon is lubricated to easeinsertion into the endoscope instrument channel. Shaft 30 of theillustrative embodiment and related embodiments has an outer diameter ofapproximately 0.085″ and an inner diameter of approximately 0.058″. Theesophageal and colonic embodiments typically have an overall length,including balloon, of approximately 420 cm, although any length that isappropriate for a particular endoscope may be used. A colonic dilationballoon catheter, for example, is typically longer, e.g., 240 cm.

Piston 52 is slideably positioned within the lumen of barrel 42 and saidpiston is secured to the distal end of elongate piston rod 54 to forminflation element 50 (FIG. 3C). Barrel 42 is transparent or translucentso that the instantaneous position of piston 52 within said barrel isobservable by the user. Piston rod handle 56 is secured to the trailingend of piston rod 54. Piston rod handle 56 facilitates force transfer tohydraulic fluid 17.

In a preferred embodiment, inflation element 50 includes a lockingmechanism for securing the inflation mechanism, and the diameter of theballoon by extension, in a preselected position. Although there arenumerous ways to lock inflation element 50 within a cylinder in multiplepositions of functional adjustment, a simple ratchet system ispreferred. The invention is not restricted to any particular lockingmeans, however, and alternate mechanisms will be apparent to the skilledartisan without departing from the contemplated invention.

In this illustrative embodiment, a plurality of ratchets, having anarrowhead or wedge shape, collectively denoted 58, is formed along apredetermined extent of piston rod 54. Each ratchet is narrow at itsleading end and wide at its trailing end to facilitateproximal-to-distal displacement of piston 52 and to substantiallyprevent inadvertent leading-to-trailing displacement. Only one (1) ofsaid ratchets 58 is internal to fluid reservoir 40 in FIG. 1 when handle56 is in a retracted position. Four (4) of said ratchets are internal tofluid reservoir 40 in FIG. 2 when said handle is in an extendedposition. Balloon 20 is inflated in FIG. 2 because piston rod handle 56has been displaced in a trailing-to-leading direction relative to itsFIG. 1 position.

Hub 60 is secured or integrally formed with the proximal or trailing endof barrel 42. As depicted in FIGS. 4A and 4B, said hub has an annularrecessed step 62 formed therein. Disc-shaped ratchet plate 64 has athickness substantially equal to a depth of step 62 so that said plate64 is substantially flush with the hub. An annular peripheral edge ofratchet plate 64 is supported by the tread of step 62.

Ratchet plate handle 65 is formed integrally with ratchet plate 34 andextends radially therefrom. Hub 60 has a cutout section formed in itsannular peripheral edge that extends about ninety degrees (90°) to allowrotation of ratchet plate handle 65 about the longitudinal axis ofsymmetry of device 10.

An elongate opening or ratchet slit 66 is formed in ratchet plate 64 inregistration with a diameter thereof. Said slit 66 is enlarged at itsmid-point 67 to accommodate piston rod 54. However, enlarged opening 67has a width less than a breadth of each ratchet 58. Accordingly, whenthe assembly is in the configuration depicted in FIG. 4A, advancingpiston rod 54 causes each ratchet 58 to momentarily compress as it isforced to pass through opening 67. The resilience of each ratchet 58causes it to return to its uncompressed position of repose after it haspassed through opening 67, as indicated by the depiction of ratchet 58in FIG. 4A. Due to the wedge or arrowhead shape of the ratchets, theycannot travel through opening 67 in a leading-to-trailing direction whenin the FIG. 4A position. Accordingly, when there is at least one (1)ratchet on the leading or distal side of opening 67, and at least one(1) ratchet on the trailing or proximal side of said opening, thenpiston 52 is locked into position. The ability to lock the piston into aplurality of positions of functional adjustment enables controlledballoon dilation.

The resistance to movement offered by ratchets 58 in aproximal-to-distal direction is not great so a user may overcome saidresistance by pushing on piston rod handle 56. A clicking sound is heardas each ratchet momentarily compresses and pops back into its positionof repose upon passing through opening 67, and the user may also feeleach ratchet passing through said opening. The user observes theposition of piston 52 relative to markings 49 to ascertain the volume offluid dispensed into balloon 20. Determination of balloon expansion (Δballoon radius) by volume transfer markings 49 provides a more accuratemeasurement than the prior art technique of monitoring system pressurewith a manometry gauge.

When retraction of piston 52 and hence deflation of balloon 20 isdesired, the user may rotate ratchet plate handle 65 to align ratchets58 with elongate opening 68 formed in ratchet plate 64, FIG. 4B.Ratchets 58 may then be withdrawn through said elongate opening in aleading-to-trailing direction.

In an alternative embodiment, shown in FIGS. 5A and 5B retraction ofpiston 52 and hence deflation of balloon 20 is achieved by rotatingpiston rod handle 56 (not shown) and hence piston rod 54 until saidratchets align with said elongate opening. Said ratchets may then bewithdrawn through said elongate opening in a leading-to-trailingdirection. A ratchet lock design that relies on rotation of the rod andpiston assembly eliminates the use of a movable ratchet plate andtherefore improves the operational simplicity and reliability of thedevice. A multiple blade rod assembly with inset ratchet notches is alsowithin the scope of this invention.

Also in a preferred embodiment, the volume of fluid reservoir 40 isadjusted at the time of manufacture with respect to the fluid volumesand pressures necessary to achieve predetermined radii of balloon 20 inits expanded state in order to accomplish progressive stricture dilationthrough controlled release of stricture wall tension. When the balloonis engaged in a stricture with a radius less than the radius of themaximally inflated balloon, wall tension is governed by the geometry ofthe stricture and not the geometry of the balloon, its elasticproperties or its material composition.

Another feature of the invention, therefore, includes a plurality ofmarkings, collectively denoted 20, imprinted upon or otherwise made apart of barrel 42. The markings of a preferred embodiment aretransversely disposed relative to a longitudinal axis of device 10 andare longitudinally spaced apart from one another. Accordingly, device 10is tuned such that volume transfer marks 20 directly correspond toincreases in system pressure within balloon 20, in accordance withPascal's principle, capable of producing controlled tension releasewithin the stricture (stretching) and thus allowing controlled unitincrease in stricture and balloon radius, in accordance with LaPlace'slaw without direct monitoring of system pressure or direct visualizationof balloon 20.

Those who have worked with prior art balloon dilation systems willappreciate the absence of any need to assemble component parts and theother advantages that flow from the novel structure. Prior art devices,for example, are filled during the dilation procedure by personnel oftenunfamiliar with sufficient mechanical experience.

Another feature of device 10, therefore, is the fact that the noveltrans-endoscopic self-contained hydraulic balloon dilation system isprovided in the form of an integrated unit so that no assembly isrequired. The invention includes the elimination of the need forassembly as well the elimination of the need to adjust the volume of thehydraulic fluid relative to the balloon. The relation of the amount offluid to the inflation of the balloon is necessary for the graduatedmarkings to give an accurate representation of balloon inflation. Theterm ‘integral’ or ‘integrated’ is not limited to a fabrication of theparts from a single piece of material, but is inclusive of other meansfor maintaining the parts fixed together as a single unit.

Moreover, fluid reservoir 40 cannot be removed from shaft 30 because itis integrally formed with the shaft. More particularly, it is directlyextruded from the fluid reservoir tube at the time of manufacture. Theextruded material may be polyethylene or any other extrudable plastic.If a manufacturer chooses to forego extrusion and to permanently glue orweld the fluid reservoir to the shaft instead, such permanent attachmentis performed at a factory and not in an operating room by untrainedpersonnel. Fluid reservoir 40 is advantageously pre-filled at the timeof manufacture with an appropriate non-toxic hydraulic fluid. Theintegrally formed, trans-endoscopic self-contained hydraulic balloonsystem thereby eliminates procedure delays incurred by componentcollection and assembly and operational errors incurred by devicecomplexity and lack of operational training. Because this insight iscontrary to the understanding, practices and expectations of the art,the structure effectuating it would not have been obvious to thoseskilled in the art when considered as a whole.

It will be seen that the advantages set forth above, and those madeapparent from the foregoing description, are efficiently attained andsince certain changes may be made in the above construction withoutdeparting from the scope of the invention, it is intended that allmatters contained in the foregoing description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense. It should be understood that the examples andembodiments described herein are for illustrative purposes only and thatvarious modifications or changes in light thereof will be suggested topersons skilled in the art and are to be included within the spirit andpurview of this application. All patents, patent applications,provisional applications and publications referred to or cited hereinare incorporated by reference in their entirety, including all figuresand tables, to the extent they are not inconsistent with the explicitteachings of this specification.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall there between.

What is claimed is:
 1. A trans-endoscopic hydraulic balloon dilationapparatus, comprising: a balloon; a hydraulic fluid reservoir having aleading end and a trailing end; an elongate hollow shaft having a lumenin open fluid communication with the balloon at a first end and thehydraulic fluid reservoir at a second end, whereby fluid in the fluidreservoir may flow through the lumen of the shaft into the balloon tocause expansion of the balloon; a centrally apertured hub secured to atrailing end of the fluid reservoir; a piston, secured to the leadingend of an elongate piston rod, slideably positioned within a lumen ofthe fluid reservoir, wherein a trailing end of the piston rod extendsthrough the hub and is external to the fluid reservoir; wherebydisplacement of the piston rod in a trailing-to-leading direction causesexpansion of the balloon; and a retention mechanism positioned on thepiston rod wherein the retention mechanism comprises a plurality ofratchet members having a flexible and resilient construction wherein theplurality of ratchet members are positioned longitudinally on the pistonrod and wherein each ratchet member is narrow at its leading end andwide at its trailing end; a disc-shaped ratchet plate disposed at atrailing end of the fluid reservoir; an elongate opening formed incenter of the disc-shaped ratchet plate wherein the elongate opening isin registration with a diameter of the ratchet plate; the elongateopening having an enlarged central portion that accommodates the pistonrod; the elongate opening central portion having a width less than abreadth of the ratchet members; the elongate opening having a lengthgreater than the breadth of the ratchet members; wherein the ratchetmembers are freely moveable through the elongate opening when theelongate opening is aligned with the ratchet members and moveable inonly one direction when the elongate opening is not in alignment withthe ratchet members; wherein when the elongate opening is not inalignment with the ratchet members, the ratchet members may bemomentarily compressed when pushed through the elongate opening centralportion for movement in only one direction; whereby the retentionmechanism locks the piston in a preselected position within the lumen ofthe fluid reservoir when the elongate opening is not aligned with theplurality of ratchet members.
 2. The apparatus of claim 1, furthercomprising: a ratchet plate handle formed integrally with the ratchetplate, the ratchet plate handle extending radially from the ratchetplate; the ratchet plate handle having a first position of rotationaladjustment when the ratchets are pushed through the central part of theelongate opening; and the ratchet plate handle having a second positionof rotational adjustment when the ratchets are aligned with the elongateopening to enable leading-to-trailing travel of the ratchets; the secondposition being about ninety degrees (90°)from the first position;whereby movement between the first position and the second positionoccurs through rotation of the ratchet plate handle in a circumferentialdirection.
 3. The apparatus of claim 1, further comprising: a piston rodhandle formed integrally with and extending radially from the pistonrod; the piston rod handle having a first position of rotationaladjustment when the ratchets are pushed through the central part of theelongate opening in a proximal-to-distal direction; the piston rodhandle having a second position of rotational adjustment when theratchets are retracted through the elongate opening in aleading-to-trailing direction.
 4. The apparatus of claim 1, furthercomprising: an annular recessed step formed in the hub; wherein theratchet plate has a thickness substantially equal to a depth of theannular recessed step so that an annular peripheral edge of the ratchetplate is supported by the annular recessed step.
 5. The apparatus ofclaim 1, wherein the fluid reservoir is substantially transparent andfurther comprises a plurality of transversely disposed, longitudinallyspaced markings provided on the fluid reservoir to facilitate visualinspection of the piston relative to the markings.
 6. The apparatus ofclaim 5, wherein the movement of the piston relative to the markingscorresponds to a predetermined volume of hydraulic fluid being expelledfrom, or drawn into, the fluid reservoir.
 7. A trans-endoscopichydraulic balloon dilation apparatus, comprising: a balloon; a hydraulicfluid reservoir having a leading end and a trailing end; an elongatehollow shaft having a lumen in open fluid communication with the balloonat a first end and the hydraulic fluid reservoir at a second end,whereby fluid in the fluid reservoir may flow through the lumen of theshaft into the balloon to cause expansion of the balloon; a centrallyapertured hub secured to a trailing end of the fluid reservoir; apiston, secured to the leading end of an elongate piston rod, slideablypositioned within a lumen of the fluid reservoir, wherein a trailing endof the piston rod extends through the hub and is external to the fluidreservoir; a plurality of transversely disposed, longitudinally spacedmarkings provided on the fluid reservoir to facilitate visual inspectionof the piston relative to the markings; the hydraulic fluid reservoir,shaft and hub forming jointly a single integral and gaplessly continuouspiece; whereby displacement of the piston rod in a trailing-to-leadingdirection causes expansion of the balloon; a retention mechanismpositioned on the piston rod wherein the retention mechanism comprises aplurality of ratchet members having a flexible and resilientconstruction wherein the plurality of ratchet members are positionedlongitudinally on the piston rod and wherein each ratchet member isnarrow at its leading end and wide at its trailing end; a disc-shapedratchet plate disposed at a trailing end of the fluid reservoir; anelongate opening formed in center of the disc-shaped ratchet platewherein the elongate opening is in registration with a diameter of theratchet plate; the elongate opening having an enlarged central portionthat accommodates the piston rod; the elongate opening central portionhaving a width less than a breadth of the ratchet members; the elongateopening having a length greater than the breadth of the ratchet members;wherein the ratchet members are freely moveable through the elongateopening when the elongate opening is aligned with the ratchet membersand moveable in only one direction when the elongate opening is not inalignment with the ratchet members; wherein when the elongate opening isnot in alignment with the ratchet members, the ratchet members may bemomentarily compressed when pushed through the elongate opening centralportion for movement in only one direction; whereby the retentionmechanism locks the piston in a preselected position within the lumen ofthe fluid reservoir when the elongate opening is not aligned with theplurality of ratchet members.
 8. The apparatus of claim 7, wherein theshaft is extruded from the fluid reservoir at the time of manufacture.9. The apparatus of claim 7, further comprising: a ratchet plate handleformed integrally with the ratchet plate, the ratchet plate handleextending radially from the ratchet plate; the ratchet plate handlehaving a first position of rotational adjustment when the ratchets arepushed through the central part of the elongate opening; and the ratchetplate handle having a second position of rotational adjustment when theratchets are aligned with the elongate opening to enableleading-to-trailing travel of the ratchets; the second position beingabout ninety degrees (90°)from the first position; whereby movementbetween the first position and the second position occurs throughrotation of the ratchet plate handle in a circumferential direction. 10.The apparatus of claim 7, further comprising: a piston rod handle formedintegrally with and extending radially from the piston rod; the pistonrod handle having a first position of rotational adjustment when theratchets are pushed through the central part of the elongate opening ina proximal-to-distal direction; the piston rod handle having a secondposition of rotational adjustment when the ratchets are retractedthrough the elongate opening in a leading-to-trailing direction.
 11. Theapparatus of claim 10, further comprising: an annular recessed stepformed in the hub wherein the ratchet plate has a thicknesssubstantially equal to a depth of the annular recessed step so that anannular peripheral edge of the ratchet plate is supported by the annularrecessed step.
 12. The apparatus of claim 7, wherein the movement of thepiston relative to the markings corresponds to a predetermined volume ofhydraulic fluid being expelled from, or drawn into, the fluid reservoir.